Conventionally, target object detection devices have been provided, in which target object detection processing, such as generation of a detection image, is executed by transmitting detection signals to a detection area, and receiving echo signals (reflection signals) of target object(s). In such target object detection devices, in addition to the echo signals of the target object(s), echo signals of clutter (reflections from sea surface, rain, etc.) may be received. Since such echo signals of the clutter cause difficulty in distinguishing the echo signal of the target object, it is desired to be suppressed.
Therefore, various methods of suppressing clutter have been devised, for example, JP3775383B discloses a multi-beam radar apparatus provided with a clutter suppressing function.
A clutter that is particularly caused by reflection from a sea surface is called a sea clutter. Suppression of the sea clutter is generally performed by acquiring echo data of a target position for a plurality of times at a predetermined time interval, and performing processing of averaging data levels of the plurality of echo data. Hereinafter, such processing is referred to as a scan correlation. By performing such processing, the echo signal of the sea clutter where high data levels seldom exist at the same position continuously in a time axis is suppressed.
However, in the conventional scan correlation, when the acquisition cycle of the echo data of the target position matches with the cycle that the sea clutter is observed at the target position at a high level, the level of data of the target position after the scan correlation will be maintained high. In such a case, sufficient clutter suppression effect cannot be obtained from the conventional scan correlation.
For example, with a radar apparatus for ships, when a cycle that a crest of a wave appears at the target position matches with the acquisition cycle of the echo data, the level of data of the target position becomes continuously high. In this case, the level of the echo signal will not be suppressed even if the scan correlation is performed, and thus, the echo signals remain as sea clutter on a detection display screen. Thus, with the conventional scan correlation, the echo signal level may not be sufficiently suppressed depending on the behavior of the sea clutter.